1. Technical Field
The present application relates to packaging for edge-sensitive cargo.
2. Background Information
Background information is for informational purposes only and does not necessarily admit that subsequently mentioned information and publications are prior art.
The present application relates to the packaging of edge-sensitive cargo. Such cargo includes glass-sheets, for example flat glass-sheets; even more sensitive are natural stone slabs. Even bending-and impact resistant laminated glass-sheets have sensitive areas. These areas are located at the edges.
Flat glass is available in various types, for example as toughened single-pane safety glass, as laminated safety glass, as laminated glass, as multi-pane composite glass, as fire protection glass, as sun protection glass, as thermally or chemically toughened glass, as float glass, as heat protection glass, as wire glass, as window glass, as cast glass, as soundproof glass, as transparent greenhouse glass. The various types of glass are largely standardized. For example, DIN 12150, DIN EN ISO 12543, DIN 1259, DIN 4102, DIN 18631 DIN 11525, DIN 11526 and DIN 52290.
Window glass is nowadays mainly produced using a float glass process, through which it achieves a high surface quality.
The float glass process is a continuous production process. Purified/refined molten glass is directed to a bath of molten tin. In comparison to the tin the glass has a lower specific gravity and therefore floats upon the molten tin. This produces very uniform glass with a high surface quality.
Laminated glass typically comprises at least two transparent layers, of which at least one is a glass sheet. Usually the other transparent sheet is also a glass sheet. Both layers are bonded together by an organic interlayer. The organic interlayer is usually a type of foil. Such foils and the connection of the glass layers are for example described in DE1292811. For example, the foils used are highly tear-resistant, tough and elastic, thermoplastic foils. Such foils comprise, for example, ethylene vinyl acetate (EVA), polyacrylate (PA), polymethyl methacrylate (PM MA), polyurethane (PUR), etc. PVB, TPU or similar materials can be used as well.
Instead of foil, other adhesive layers such as liquid resins might be used. Laminated glass also includes glass-sheets that are bonded to other materials, such as a transparent polycarbonate.
Glass, with comparable properties like laminated glass, usually has a substantial thickness. To generate a stress-relieved state, such a glass is for example produced stress-free or heat-treated after production. In its stress-relieved state, the glass is highly rigid and impact resistant in comparison to other conventionally produced glass. If an edge-protection for laminated glass is addressed in the remainder of this document, the expression laminated glass also includes one-piece glass with similar properties.
Laminated glass-sheets have found manifold applications. Possibly known are the applications in construction and in automotive technology. In automotive technology, the laminated glass-sheets are also known as safety glass.
In construction, laminated glass-sheets are for example used for shop windows, large-surface windows, glass doors, large-surface glass doors, shower enclosures, balustrades, transparent partitioning walls, overhead glazing, glass roofing and glass porches or the like.
Laminated glass can fulfill multiple tasks. Of these, rigidness and impact resistance are two of the possible tasks. Other possible tasks include fire protection or sound insulation.
When compared to a single-sheet, laminated glass-sheets distinguish themselves through characteristics such as a very high rigidness and a high impact resistance. Rigidness and impact resistance are not defined as absolute values, but rather as values that are sufficient for the possible application for which the laminated glass is used.
It is also used in considerable volumes for other types of glass such as toughened safety glass, insulating-glass, mirror-glass and other types of glass.
Despite its strength, the edges of glass, including laminated glass, may be sensitive.
Therefore it is common, not only with a simple type of glass but also with laminated glass and other types of glass, to protect glass-sheets very well, for example for transport. Possibly in construction, one cannot expect that glass be handled with extreme caution. The harsh modus operandi of the construction business is not set up for such precaution. Up until now, substantial damage to glass is a regular phenomenon in construction. Up to ten percent damages is quite common and even twenty percent is not regarded as exceptional.
Laminated glass-sheets for motor vehicles are usually box- or crate-protected in multiples, i.e. placed in a protective box or crate. In this case, a soft, flexible bed is prevised in the boxes. The boxes are designed to transport the laminated glass from the manufacturer to a vehicle manufacturer or to a vehicle repair shop.
The dimensions of glass-sheets designated for use in construction often have much larger dimensions than the glass used for motor vehicles. Therefore, it is common to transport glass-sheets for constructional use to the construction site in an upright position in a so-called load carrier. A load-carrier is a frame in which the glass-sheets are transported in an upright position. There are vehicles with fixed load-carriers. Frequently, the glass is offloaded from the load-carrier at a construction site. Using a load-carrier has major drawbacks:
A vehicle that is equipped as a load-carrier is not suitable for other transports.
The vehicle must or should wait at the construction site until all or most the glass sheets are installed, or a safe interim storage for the glass-sheets must or should be created on site.
The load-carriers are rigid racks that are mountable i.e. lockable on vehicles, in which glass is secured in an upright position. The transport costs for such rack-systems are disproportionately high. In addition it must or should be taken into account that the racks must or should not only be transported to the construction site, but also need to be collected or should be collected from the construction site again. Furthermore it must or should be taken into account that trucks commonly used for glass transport, when loaded with racks and glass, are filled nowhere near to maximum capacity. It is not uncommon to see offers for glass transport, where the cost of transport is just as high as the cost of the glass itself.
A vehicle with an off loadable load-carrier is of course suitable for other tasks. However, the load-carriers consume a lot of cargo space and are a great hindrance for additional cargo. The load-carrier is offloaded at the construction site. After installing the glass-sheets, the carrier must or should be collected again. Both issues result in high transport costs. In addition, if a load-carrier is not immediately or substantially immediately released, this usually creates significant additional costs. If a delay in the installation of the glass-sheets occurs, a delayed release of the load-carrier is an automatic consequence. In that case, one wants to continue to store the glass on the load-carriers, because any other type of storage contains a much greater risk of damage to the glass.
Cargo that is partially made of glass encounters the same problems as described for glass sheets above. This is the case for example with photovoltaic elements/solar cells.
With natural stone slabs a similar situation as for glass-sheets exists. However, because of their inhomogeneity, natural stone slabs with the same thickness are even more sensitive than glass. Thin Natural stone slabs will break at the slightest bending load. Natural stone slabs are also transported to the customer placed upright in a load-carrier. In construction, natural stone slabs are often used as well, for example as floor panels and windowsills.
However, also other cargo is easily damaged. These include for example countertops that are otherwise able to withstand considerable loads, but are highly sensitive along their sharp edges.
For much cargo, edge-sensitivity is the most frequent cause of damages.
This applies not only to other sheet-like cargo, but also to cuboidal cargo.